In many fields, investigations are being made into inorganic materials having lighter weight and a wider range of material selection than those of known inorganic materials. Since most π-conjugated polymers are polymers having conductivity and potentially have properties utilizable in various kinds of electronic materials, optical functional materials, and magnetic functional materials, studies for application of the π-conjugated polymers to various fields are energetically being conducted (for example, see Y. Saito et al., Journal of Photochemistry And Photobiology A: Chemistry (J. Photochem. Photobiol. A: Chem.), 2004, Vol. 164, p. 153; and Y. Shibata et al., Chemical Communications (Chem. Commun.), 2003, p. 2730 and 2731).
Polymer conductivity (σ) is expressed by Expression (1) as the product of a density (n) of mobile carriers (electrons) in the polymer, a mobility (μ) representing the ease of carrier movement, and the electronic charge (e) as follows.σ=enμ  Expression (1)
Accordingly, any one of a method of enhancing the carrier density ‘n’ in a material and a method of improving the mobility μ is used in order to enhance the conductivity (σ). In general, the π conjugated polymer has semiconductor-like conductivity and the conductivity is determined by energy levels of the top of the valence band (HOMO: highest occupied molecular orbital) and the bottom of the conduction band (LUMO: lowest unoccupied molecular orbital) determined by a molecular structure of the polymer, a width (a width of a forbidden band) between the HOMO and the LUMO, and the energy level of impurities doped in the forbidden band. Here, although the carrier density can be controlled by the doping in a relatively easy manner, the carrier density is generally reversible in the atmosphere. Meanwhile, the mobility changes greatly by the molecular structure, conformation, packing between polymer chains, crystalline properties, and the like, and thus it is difficult to control or enhance the mobility.